Diabetes medications fall into several distinct classes, each lowering blood sugar through a different mechanism. The right choice depends on factors like your type of diabetes, heart and kidney health, weight goals, and how your body responds to treatment. Metformin remains the standard first-line medication for type 2 diabetes, but newer drug classes have expanded the options significantly.
Metformin
Metformin is the most widely prescribed diabetes medication in the world and typically the first one doctors reach for. It works primarily by reducing the amount of sugar your liver produces and releases into your bloodstream. It also improves how your muscles use insulin and may slow sugar absorption in your gut. Most people can expect their A1c (a measure of average blood sugar over three months) to drop by about 1 to 1.5 percentage points on metformin alone.
The most common side effects are digestive: nausea, bloating, and diarrhea, especially in the first few weeks. An extended-release version often reduces these issues. Metformin does not cause low blood sugar on its own and is weight-neutral or slightly favorable for weight loss, which is one reason it has stayed at the top of treatment guidelines for decades.
GLP-1 Receptor Agonists
GLP-1 receptor agonists mimic a gut hormone called GLP-1 that your body naturally releases after eating. They trigger insulin release from the pancreas, slow digestion, and act on areas of the brain that process hunger and fullness. The result is lower blood sugar and, for many people, meaningful weight loss.
Medications in this class include semaglutide (sold as Ozempic for injection and Rybelsus as a tablet), liraglutide (Victoza), dulaglutide (Trulicity), exenatide (Byetta and the extended-release Bydureon), and lixisenatide (Adlyxin). Most are weekly injections, though the oral semaglutide tablet is an option for people who prefer not to inject.
Nausea is the most common side effect, particularly when starting or increasing the dose. It usually fades over a few weeks. Current guidelines recommend GLP-1 agonists as a first-line option alongside metformin for people who have cardiovascular disease or chronic kidney disease, because certain drugs in this class have been shown to reduce heart attack and stroke risk.
SGLT2 Inhibitors
SGLT2 inhibitors take a completely different approach: they block a protein in your kidneys that normally reabsorbs sugar back into your blood. The excess sugar is then flushed out through urine. Common medications include empagliflozin (Jardiance), dapagliflozin (Farxiga), canagliflozin (Invokana), ertugliflozin (Steglatro), and bexagliflozin (Brenzavvy).
Beyond blood sugar control, this class has proven benefits for heart and kidney health. SGLT2 inhibitors can slow the progression of kidney disease, reduce the risk of needing dialysis, and lower the risk of heart failure flare-ups. For people with heart failure or chronic kidney disease, guidelines now recommend starting with an SGLT2 inhibitor regardless of blood sugar levels. Side effects can include urinary tract infections and genital yeast infections, since more sugar in the urine creates an environment where bacteria and yeast thrive.
Dual GIP/GLP-1 Agonists
Tirzepatide (Mounjaro) represents a newer approach. It activates two incretin hormone receptors at once: GLP-1 and GIP. Both hormones help regulate blood sugar after meals, but they work through partially independent pathways. By targeting both receptors, tirzepatide enhances insulin secretion, improves insulin sensitivity through a mechanism that appears to be independent of weight loss, and produces substantial appetite suppression.
In clinical trials, tirzepatide delivered larger reductions in both A1c and body weight than single-target GLP-1 drugs. Like GLP-1 agonists, the most common side effects are gastrointestinal: nausea, diarrhea, and reduced appetite, particularly during dose increases.
DPP-4 Inhibitors
DPP-4 inhibitors work on the same incretin system as GLP-1 agonists, but more gently. Your body naturally produces GLP-1 and another hormone called GIP after meals. An enzyme called DPP-4 breaks these hormones down quickly. DPP-4 inhibitors block that enzyme, letting your own incretin hormones stay active longer. The result is more insulin when blood sugar is high and less glucagon (a hormone that raises blood sugar).
Options include sitagliptin (Januvia), saxagliptin (Onglyza), linagliptin (Tradjenta), and alogliptin (Nesina). Several combination pills pair a DPP-4 inhibitor with metformin, such as Janumet and Jentadueto. These medications are taken orally, are generally well tolerated with few gastrointestinal side effects, and don’t cause weight gain. The tradeoff is that their blood sugar lowering effect is more modest than GLP-1 agonists or SGLT2 inhibitors.
Sulfonylureas and Meglitinides
Both of these older classes work by stimulating the pancreas to release more insulin, but they differ in timing. Sulfonylureas (like glipizide, glyburide, and glimepiride) push the pancreas to secrete insulin over several hours. Meglitinides (like repaglinide and nateglinide) trigger a shorter burst of insulin timed around meals.
The main concern with both is hypoglycemia, or low blood sugar. Because they stimulate insulin regardless of whether blood sugar is actually high, skipping a meal or eating less than usual can cause a dangerous drop. This risk is higher in older adults and people with kidney problems, since the kidneys clear these drugs from the body more slowly. Both classes also tend to promote weight gain. They remain in use because they’re inexpensive and effective at lowering A1c, but they’ve been largely displaced by newer medications with better safety profiles.
Thiazolidinediones
Thiazolidinediones, often called TZDs, improve how your fat, muscle, and liver cells respond to insulin. They activate receptors involved in metabolism, making those cells better at pulling sugar out of your blood. The two available TZDs are pioglitazone (Actos) and rosiglitazone (Avandia).
TZDs can be effective for people with significant insulin resistance, but they come with notable side effects: weight gain, fluid retention, and an increased risk of bone fractures. Pioglitazone is the more commonly prescribed of the two, as rosiglitazone faced restrictions years ago over cardiovascular safety concerns.
Alpha-Glucosidase Inhibitors
Alpha-glucosidase inhibitors take aim at carbohydrate digestion itself. They block enzymes in your small intestine that break down complex carbohydrates into sugar, slowing the rate at which glucose enters your bloodstream after a meal. The two FDA-approved options are acarbose (Precose) and miglitol (Glyset).
These medications are particularly useful for controlling post-meal blood sugar spikes. They don’t cause hypoglycemia on their own and are weight-neutral. The downside is significant gas, bloating, and diarrhea, since undigested carbohydrates ferment in the large intestine. These effects limit their popularity, though starting at a low dose and increasing gradually can help.
Insulin
Everyone with type 1 diabetes needs insulin, and many people with type 2 diabetes eventually need it as well, particularly as the disease progresses and the pancreas produces less on its own. Insulin comes in several categories based on how quickly it starts working and how long it lasts:
- Rapid-acting: Starts working in about 15 minutes, peaks at 1 hour, and lasts 2 to 4 hours. Taken just before or with meals.
- Short-acting (regular): Starts in 30 minutes, peaks at 2 to 3 hours, lasts 3 to 6 hours.
- Intermediate-acting: Starts in 2 to 4 hours, peaks between 4 and 12 hours, lasts 12 to 18 hours.
- Long-acting: Starts in about 2 hours, has no sharp peak, and provides a steady level of insulin for up to 24 hours.
Most people with type 2 diabetes who need insulin start with a long-acting form taken once daily. If that’s not enough, rapid-acting insulin at mealtimes may be added. The primary risks are hypoglycemia and weight gain. Insulin delivery has improved considerably with pre-filled pens and, for some, insulin pumps that provide continuous dosing.
How Doctors Choose Between Them
Treatment guidelines follow a clear logic. Metformin is still the starting point for most people with type 2 diabetes who don’t have heart or kidney complications. If you do have cardiovascular disease or high cardiovascular risk, a GLP-1 agonist or SGLT2 inhibitor with proven heart benefits is recommended from the start. If heart failure is the concern, SGLT2 inhibitors are preferred. For chronic kidney disease, SGLT2 inhibitors are first choice, with GLP-1 agonists as the backup if those aren’t tolerated.
Many people end up on a combination of two or more medications from different classes. For example, someone might take metformin alongside an SGLT2 inhibitor and a GLP-1 agonist, each addressing blood sugar through a different pathway. The trend in diabetes treatment has shifted away from simply lowering blood sugar numbers and toward choosing medications that also protect the heart, kidneys, and overall metabolic health.